1. Field of the Invention
The present invention relates to an automatic focus adjustment apparatus for a photographic camera, and more particularly to an automatic focus adjustment apparatus capable of rapidly driving a photographing lens to a desired focus position.
2. Related Background Art
It has heretofore been known that a photographic camera of the type provided with an automatic focus adjustment apparatus commonly includes a function which is called "focus lock". One typical example of such photographic cameras is arranged such that, when its photographing lens is focused on an object during the operation of a shutter release button in its halfway depressed state, the focusing operation of the photographing lens is locked as long as the shutter release button continues to be halfway depressed. Another typical example is arranged such that its photographing lens is continuously driven toward the in-focus position in accordance with the motion of an object during the operation of a shutter release button in its halfway depressed state, the photographing lens being locked at a desired focus position by a focus-lock operation member which is provided separately from the shutter release button.
The former type of focus lock is arranged to be cancelled by stopping the operation of the shutter release button in its halfway depressed state while the latter type of focus lock is arranged to be cancelled by stopping the operation of the focus-lock operation member.
While the focus position of the aforesaid conventional type of photographic camera is being locked with respect to a first object by the operation of its focus lock, a photographer may try to rapidly take a picture of a second object. In the case of the former type of focus lock, after the photographer has removed his finger from the shutter release button, he must again depress it halfway to bring the second object into focus. In the case of the latter type of focus lock, after the photographer has stopped the operation of the focus lock member, he must focus his camera on the second object. In either case, it is necessary to clear the in-focus position which was previously locked with respect to the first object. Therefore, the photographer must again operate the shutter release button in its halfway depressed state so as to bring the first object into focus and then perform a focus-lock operation. This forces the photographer into an awkward photographic operation.